Genetic studies have shown that wild-type-D-serine deaminase (Dsdase I, dsdA gene product) synthesis in Escherichia coli K12 is controlled by induction and catabolite repression, at the level of transcription. The induction control, which is mediated by the dsdC gene product, appears to be strictly positive. The catabolite repression control is mediated by the cyclic AMP and cyclic AMP binding protein system. The operator locus, dsdO, is the site of action of both the induction and the catabolite repression controls. A second D-serine deaminase, Dsdase II, with relatively low activity in the deaminating reaction is formed by E. coli K12. Bibliographic references: Heincz, M.C. and McFall, E. 1975. A second D-serine deaminase in Escherichia coli K12. (Abstract No. 2534). Fed. Proc. 34, 665. Heincz, M.C. and McFall, E. 1975. N-terminal amino acid sequences of wild-type and operator-constitutive strains of Escherichia coli K12. J. Bacteriol. 123, 1163-1168.